U.S. patent application number 13/344294 was filed with the patent office on 2012-07-12 for electric power steering apparatus.
This patent application is currently assigned to HONDA MOTOR CO., LTD.. Invention is credited to Kyoji HAMAMOTO, Shinji HIRONAKA, Hiroaki HORII, Takashi KURIBAYASHI, Fumihiro MORISHITA, Hiroki SAGAMI, Takuji WADA.
Application Number | 20120176069 13/344294 |
Document ID | / |
Family ID | 46454758 |
Filed Date | 2012-07-12 |
United States Patent
Application |
20120176069 |
Kind Code |
A1 |
SAGAMI; Hiroki ; et
al. |
July 12, 2012 |
ELECTRIC POWER STEERING APPARATUS
Abstract
An electric power steering apparatus detects, as an abnormal
phase, a phase other than a combination of phases whose interphase
voltage is of nearly zero volts if a q-axis current is equal to or
smaller than a first threshold value though a q-axis voltage is
being applied. Alternatively, the electric power steering apparatus
calculates a base electric angle at which the q-axis current is
equal to or smaller than a third threshold value though the q-axis
voltage is being applied, and determines an abnormal phase based on
the base electric angle.
Inventors: |
SAGAMI; Hiroki;
(UTSUNOMIYA-SHI, JP) ; HAMAMOTO; Kyoji;
(UTSUNOMIYA-SHI, JP) ; HORII; Hiroaki;
(UTSUNOMIYA-SHI, JP) ; MORISHITA; Fumihiro;
(TOCHIGI-KEN, JP) ; WADA; Takuji; (UTSUNOMIYA-SHI,
JP) ; HIRONAKA; Shinji; (TOCHIGI-KEN, JP) ;
KURIBAYASHI; Takashi; (TOCHIGI-KEN, JP) |
Assignee: |
HONDA MOTOR CO., LTD.
TOKYO
JP
|
Family ID: |
46454758 |
Appl. No.: |
13/344294 |
Filed: |
January 5, 2012 |
Current U.S.
Class: |
318/400.02 |
Current CPC
Class: |
B62D 5/0487
20130101 |
Class at
Publication: |
318/400.02 |
International
Class: |
H02P 6/12 20060101
H02P006/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 7, 2011 |
JP |
2011-002522 |
Jan 7, 2011 |
JP |
2011-002523 |
Claims
1. An electric power steering apparatus comprising: an inverter for
supplying three-phase AC electric power to three phases of an
electric motor; a current coordinate converting unit for converting
currents flowing in the three phases of the electric motor into d-q
coordinate currents including a d-axis current as an exciting
current component and a q-axis current as a torque current
component; a voltage coordinate converting unit for converting
three-phase voltages applied to the electric motor into a d-axis
voltage and a q-axis voltage; and an abnormal phase detecting unit
for detecting, as an abnormal phase, a phase other than a
combination of phases whose interphase voltage is of nearly zero
volts in a state where the q-axis current is equal to or smaller
than a first threshold value though the q-axis voltage is being
applied.
2. The electric power steering apparatus according to claim 1,
further comprising: a rotational speed detecting unit for detecting
a rotational speed of the electric motor; wherein the abnormal
phase detecting unit is operated when the rotational speed is equal
to or smaller than a second threshold value.
3. The electric power steering apparatus according to claim 1,
wherein if the abnormal phase detecting unit detects an abnormal
phase while all the three phases are being energized, the phases
other than the abnormal phase are energized such that output power
of the electric motor is increased near an electric angle at which
the output power of the electric motor tends to be reduced due to
malfunctioning of the abnormal phase.
4. An electric power steering apparatus comprising: an inverter for
supplying three-phase AC electric power to three phases of an
electric motor; a current coordinate converting unit for converting
currents flowing in the three phases of the electric motor into d-q
coordinate currents including a d-axis current as an exciting
current component and a q-axis current as a torque current
component; a voltage coordinate converting unit for converting
three-phase voltages applied to the electric motor into a d-axis
voltage and a q-axis voltage; and a rotational angle detecting unit
for detecting a rotational angle of the electric motor; wherein a
base electric angle at which the q-axis current is equal to or
smaller than a third threshold value though the q-axis voltage is
being applied is calculated; and an abnormal phase is determined
based on the base electric angle.
5. The electric power steering apparatus according to claim 4,
wherein while the d-axis voltage is being generated, a corrective
electric angle is calculated from the d-axis voltage and the q-axis
voltage; and an abnormal phase is determined based on the base
electric angle and the corrective electric angle.
6. The electric power steering apparatus according to claim 4,
further comprising: a rotational speed detecting unit for detecting
a rotational speed of the electric motor; wherein an abnormal phase
is determined if the rotational speed is equal to or smaller than a
fourth threshold value.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority from Japanese Patent Applications No. 2011-002522 filed on
Jan. 7, 2011, and No. 2011-002523 filed on Jan. 7, 2011, of which
the contents are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to an electric power steering
apparatus which includes an electric motor that applies a force
(steering assisting force) for assisting in a steering action made
by the driver of a motor vehicle when the driver turns the steering
wheel of the motor vehicle.
[0004] 2. Description of the Related Art
[0005] There are known electric power steering apparatus which
include an electric motor that applies a force (steering assisting
force) for assisting in a steering action made by the driver of a
motor vehicle in order to allow the driver to lightly turn the
steering wheel of the motor vehicle {see U.S. Patent Application
Publication No. 2007/0176577 (hereinafter referred to as "US
2007/0176577 A1"), Japanese Laid-Open Patent Publication No.
2009-090817 (hereinafter referred to as "JP 2009-090817 A1"), and
Japanese Laid-Open Patent Publication No. 2006-256542 (hereinafter
referred to as "JP 2006-256542 A1")}.
[0006] According to US 2007/0176577 A1, currents for the respective
three phases of an electric motor are detected (see [0055] through
[0058] and FIG. 17), and it is judged whether such currents are
flowing or not, whereby it is determined whether there is a phase
with an abnormality (abnormal phase) or not (see [0059] through
[0060]). If an abnormal phase occurs, then the switching devices of
an inverter are controlled with respect to the normal phases other
than the abnormal phase (see Abstract and claims 15, 17).
[0007] According to JP 2009-090817 A1, currents for two of the
three phases (a U-phase current and a W-phase current) are
detected, and a current for one remaining phase is calculated from
the detected currents for the two phases and used for subsequent
inverter control (see FIG. 2 and [0023]). According to JP
2006-256542 A1, similarly, currents for two of the three phases (a
U-phase current and a V-phase current) are detected, and a current
for one remaining phase is calculated from the detected currents
for the two phases and used for subsequent inverter control (see
FIG. 2, [0012] and [0018]).
SUMMARY OF THE INVENTION
[0008] As described above, according to US 2007/0176577 A1, an
abnormal phase is identified by detecting currents for the
respective three phases. With the arrangements for detecting
currents for two of the three phases as disclosed in JP 2009-090817
A1 and JP 2006-256542 A1, however, it is difficult to identify an
abnormal phase if an abnormality such as a disconnection or the
like happens to any of the phases.
[0009] It is an object of the present invention to provide an
electric power steering apparatus which is capable of detecting an
abnormal phase of an electric motor thereof even in the case where
currents for two of the three phases are detected.
[0010] According to the present invention, there is provided an
electric power steering apparatus comprising an inverter for
supplying three-phase AC electric power to three phases of an
electric motor, a current coordinate converting unit for converting
currents flowing in the three phases of the electric motor into d-q
coordinate currents including a d-axis current as an exciting
current component and a q-axis current as a torque current
component, a voltage coordinate converting unit for converting
three-phase voltages applied to the electric motor into a d-axis
voltage and a q-axis voltage, and an abnormal phase detecting unit
for detecting, as an abnormal phase, a phase other than a
combination of phases whose interphase voltage is of nearly zero
volts in a state where the q-axis current is equal to or smaller
than a first threshold value though the q-axis voltage is being
applied.
[0011] With the above arrangement, a phase other than a combination
of phases whose interphase voltage is of nearly zero volts is
detected as an abnormal phase in a state where the q-axis current
is equal to or smaller than a first threshold value though the
q-axis voltage is being applied. Therefore, if a value (e.g., zero
or a value near zero) that cannot be taken depending on the q-axis
voltage is established as the first threshold value for the q-axis
current, then an abnormal phase can be detected even though current
sensors are provided in association with only two phases and no
current sensor is provided in association with the remaining phase.
The invention is also applicable to an arrangement wherein current
sensors are provided in association with all the three phases for
the purpose of increasing the accuracy with which to detect an
abnormal phase.
[0012] The electric power steering apparatus may further comprise a
rotational speed detecting unit for detecting a rotational speed of
the electric motor, and the abnormal phase detecting unit may be
operated when the rotational speed is equal to or smaller than a
second threshold value. If a rotational speed at which a
counter-electromotive force generated by the electric motor
adversely affects the accuracy with which to identify an abnormal
phase, or a nearby rotational speed is established as the second
threshold value, then an abnormal phase can be identified only when
a certain level of accuracy is secured. An abnormal phase is thus
prevented from being detected in error.
[0013] If the abnormal phase detecting unit detects an abnormal
phase while all the three phases are being energized, the phases
other than the abnormal phase are energized such that output power
of the electric motor is increased near an electric angle at which
the output power of the electric motor tends to be reduced due to
malfunctioning of the abnormal phase. Therefore, even in the
presence of an abnormal phase, the output power of the electric
motor is prevented from being abruptly lowered, and hence the
electric motor is capable of stably generating a steering assisting
force.
[0014] According to the present invention, there is also provided
an electric power steering apparatus comprising an inverter for
supplying three-phase AC electric power to three phases of an
electric motor, a current coordinate converting unit for converting
currents flowing in the three phases of the electric motor into d-q
coordinate currents including a d-axis current as an exciting
current component and a q-axis current as a torque current
component, a voltage coordinate converting unit for converting
three-phase voltages applied to the electric motor into a d-axis
voltage and a q-axis voltage, and a rotational angle detecting unit
for detecting a rotational angle of the electric motor, wherein a
base electric angle at which the q-axis current is equal to or
smaller than a third threshold value though the q-axis voltage is
being applied is calculated, and an abnormal phase is determined
based on the base electric angle.
[0015] With the above arrangement, a base electric angle at which
the q-axis current is equal to or smaller than a third threshold
value though the q-axis voltage is being applied is calculated, and
an abnormal phase is determined based on the base electric angle.
Therefore, if a value (e.g., zero or a value near zero) that cannot
be taken if the phases are operating normally is established as the
third threshold value, then an abnormal phase can be detected even
though current sensors are provided in association with only two
phases and no current sensor is provided in association with the
remaining phase. The invention is also applicable to an arrangement
wherein current sensors are provided in association with all the
three phases for the purpose of increasing the accuracy with which
to detect an abnormal phase.
[0016] While the d-axis voltage is being generated, a corrective
electric angle may be calculated from the d-axis voltage and the
q-axis voltage, and an abnormal phase may be determined based on
the base electric angle and the corrective electric angle.
Therefore, even if the electric angle at which the q-axis current
is equal to or smaller than the third threshold due to the
generation of the d-axis voltage deviates from the base electric
angle, it is possible to correct the base electric angle in view of
the effect of the d-axis voltage. Therefore, an abnormal phase can
be determined highly accurately.
[0017] The electric power steering apparatus may further comprise a
rotational speed detecting unit for detecting a rotational speed of
the electric motor, and an abnormal phase may be determined if the
rotational speed is equal to or smaller than a fourth threshold
value. Therefore, if a rotational speed at which a
counter-electromotive force generated by the electric motor
adversely affects the accuracy with which to identify an abnormal
phase, or a nearby rotational speed is established as the fourth
threshold value, then an abnormal phase can be identified only when
a certain level of accuracy is secured. An abnormal phase is thus
prevented from being detected in error.
[0018] The above and other objects, features, and advantages of the
present invention will become more apparent from the following
description when taken in conjunction with the accompanying
drawings in which preferred embodiments of the present invention
are shown by way of illustrative example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a schematic view, partly in block form, of an
electric power steering apparatus according to a first embodiment
of the present invention;
[0020] FIG. 2 is a circuit diagram of parts of the electric power
steering apparatus according to the first embodiment;
[0021] FIG. 3 is a block diagram showing internal configurations
and functions of an electronic control unit (ECU) and input and
output lines connected to the ECU according to the first
embodiment;
[0022] FIG. 4 is a flowchart of a processing sequence of the ECU
according to the first embodiment;
[0023] FIG. 5 is a functional block diagram of the ECU in a normal
energization controlling mode;
[0024] FIG. 6 is a diagram showing, by way of example, waveforms
representing the torques of respective phases of the electric
motor, a steering assisting torque, and the currents of the
respective phases in the normal energization controlling mode;
[0025] FIG. 7 is a flowchart of an abnormality determining process
carried out by the ECU according to the first embodiment;
[0026] FIG. 8 is a flowchart of an abnormal phase identifying
process carried out by the ECU according to the first
embodiment;
[0027] FIG. 9 is a functional block diagram of the ECU according to
the first embodiment in an abnormality-occurring energization
controlling mode;
[0028] FIG. 10 is a functional block diagram of a gain setting
section of the ECU according to the first embodiment;
[0029] FIG. 11 is a diagram showing a relationship between electric
angles of the electric motor and output voltages of the respective
phases thereof in the abnormality-occurring energization
controlling mode in the event of an abnormality that occurs in a
U-phase;
[0030] FIG. 12 is a diagram showing a relationship between electric
angles of the electric motor and output voltages of the respective
phases thereof in the abnormality-occurring energization
controlling mode in the event of an abnormality that occurs in a
V-phase;
[0031] FIG. 13 is a diagram showing the relationship between
electric angles of the electric motor and output voltages of the
respective phases thereof in the abnormality-occurring energization
controlling mode in the event of an abnormality that occurs in a
W-phase;
[0032] FIG. 14 is a flowchart of an abnormality determining process
carried out by an ECU according to a second embodiment of the
present invention;
[0033] FIG. 15 is a diagram showing, by way of example, waveforms
of a V-phase current and a W-phase current at the time a d-axis
voltage is zero in the event of an abnormality that occurs in a
U-phase;
[0034] FIG. 16 is a diagram showing, by way of example, waveforms
of a V-phase current and a W-phase current at the time the d-axis
voltage is not zero in the event of the abnormality that occurs in
the U-phase;
[0035] FIG. 17 is a diagram showing a relationship between a d-axis
voltage Vd, a q-axis voltage Vq, and a corrective electric
angle;
[0036] FIG. 18 is a flowchart of an abnormal phase identifying
process carried out by the ECU according to the second
embodiment;
[0037] FIG. 19 is a diagram showing a first modification of the
relationship between electric angles of the electric motor and
output voltages of the respective phases thereof in the
abnormality-occurring energization controlling mode;
[0038] FIG. 20 is a diagram showing a second modification of the
relationship between electric angles of the electric motor and
output voltages of the respective phases thereof in the
abnormality-occurring energization controlling mode;
[0039] FIG. 21 is a diagram showing a third modification of the
relationship between electric angles of the electric motor and
output voltages of the respective phases thereof in the
abnormality-occurring energization controlling mode;
[0040] FIG. 22 is a diagram showing a fourth modification of the
relationship between electric angles of the electric motor and
output voltages of the respective phases thereof in the
abnormality-occurring energization controlling mode;
[0041] FIG. 23 is a diagram showing a fifth modification of the
relationship between electric angles of the electric motor and
output voltages of the respective phases thereof in the
abnormality-occurring energization controlling mode; and
[0042] FIG. 24 is a diagram showing a sixth modification of the
relationship between electric angles of the electric motor and
output voltages of the respective phases thereof in the
abnormality-occurring energization controlling mode.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
I. First Embodiment
A: Description of Configurations
1. Overall Arrangement of Electric Power Steering Apparatus 10:
[0043] FIG. 1 is a schematic view, partly in block form, of an
electric power steering apparatus 10 (hereinafter also referred to
as "power steering apparatus 10") according to a first embodiment
of the present invention, which is incorporated in a motor vehicle.
FIG. 2 is a circuit diagram of parts of the electric power steering
apparatus 10.
[0044] As shown in FIG. 1, the power steering apparatus 10 includes
a steering handle 12 (steering wheel), a steering shaft 14, a rack
shaft 16, tie rods 1, and left and right front road wheels 20 as
steerable wheels of the motor vehicle. The steering shaft 14, the
rack shaft 16, and the tie rods 18 make up a manual steering system
for directly transmitting a steering action that is applied to the
steering handle 12 by the driver of the motor vehicle, to the front
road wheels 20.
[0045] As shown in FIGS. 1 and 2, the power steering apparatus 10
also includes an electric motor 22, a worm gear 24, a worm wheel
gear 26, a torque sensor 28, a vehicle speed sensor 30, a steering
angle sensor 32, a battery 34, an inverter 36, current sensors 38,
40, a resolver (rotational angle detecting unit) 42, voltage
sensors 44, 46, 48, and an electronic control unit 50 (hereinafter
referred to as "ECU 50"). The electric motor 22, the worm gear 24,
and the worm wheel gear 26 make up an assistive drive system for
generating a force (steering assisting force) for assisting in the
steering action made by the driver. The torque sensor 28, the
vehicle speed sensor 30, the steering angle sensor 32, the inverter
36, the current sensors 38, 40, the resolver 42, the voltage
sensors 44, 46, 48, and the ECU 50 make up an assistive control
system for controlling the assistive drive system. The assistive
drive system, the assistive control system, and the battery 34 will
hereinafter also be collectively referred to as "steering assisting
system".
2. Manual Steering System:
[0046] The steering shaft 14 includes a main steering shaft 52
integrally coupled to the steering handle 12, a pinion shaft 54
having a pinion 56 of a rack and pinion mechanism, and universal
joints 58 interconnecting the main steering shaft 52 and the pinion
shaft 54.
[0047] The pinion shaft 54 has an upper portion, an intermediate
portion, a lower portion, which are supported respectively by
bearings 60a, 60b and 60c. The pinion 56 is disposed on a lower end
portion of the pinion shaft 54. The pinion 56 is held in mesh with
rack teeth 62 of the rack shaft 16 that is movable axially back and
forth in transverse directions of the motor vehicle.
[0048] When the driver turns the steering handle 12, the steering
handle 12 produces a steering torque Tr (rotary force), which is
transmitted to the pinion shaft 54 through the main steering shaft
52 and the universal joints 58. The pinion 56 of the pinion shaft
54 and the rack teeth 62 of the rack shaft 16 convert the steering
torque Tr into a thrust force, which displaces the rack shaft 16 in
the transverse directions of the motor vehicle. When the rack shaft
16 is displaced, the tie rods 18 steer the front road wheels 20 to
change the direction of the motor vehicle.
3. Steering Assisting System:
(1) Assistive Drive System:
[0049] The electric motor 22 is operatively connected to the rack
shaft 16 through the worm gear 24 and the worm wheel gear 26. More
specifically, the electric motor 22 has an output shaft 22a
connected to the worm gear 24. The worm wheel gear 26 which is in
mesh with the worm gear 24 is mounted on the pinion shaft 54, which
is operatively connected to the rack shaft 16 through the pinion 56
and the rack teeth 62.
[0050] The electric motor 22, which is a three-phase AC brushless
motor, is supplied with electric power from the battery 34 via the
inverter 36 that is controlled by the ECU 50, and generates a drive
force (steering assisting force) depending on the electric power.
The drive force is transmitted through the output shaft 22a, the
worm gear 24, and the pinion shaft 54 (the worm wheel gear 26 and
the pinion 56) to the rack shaft 16, thereby assisting the driver
in turning the steering handle 12.
(2) Assistive Control System:
(a) Feed-Forward System Sensors:
[0051] The torque sensor 28 is disposed between the bearing 60a on
the upper portion of the pinion shaft 54 and the bearing 60b on the
intermediate portion of the pinion shaft 54. The torque sensor 28
detects a steering torque Tr based on a change in magnetic
characteristics caused by a magnetostrictive effect, and outputs
the detected steering torque Tr to the ECU 50.
[0052] The vehicle speed sensor 30 detects a vehicle speed V [km/h]
and outputs the detected vehicle speed V to the ECU 50. The
steering angle sensor 32 detects a steering angle .theta.s
[degrees] of the steering handle 12 and outputs the detected
steering angle .theta.s to the ECU 50.
[0053] The steering torque Tr, the vehicle speed V, and the
steering angle .theta.s are used in a feed-forward control process
by the ECU 50.
(b) Inverter 36:
[0054] The inverter 36, which is of a three-phase bridge
configuration, has a DC-to-AC converting capability which converts
a direct current from the battery 34 into three-phase alternating
currents and supplies the three-phase alternating currents to the
electric motor 22.
[0055] As shown in FIG. 2, the inverter 36 has three-phase arms
70u, 70v, 70w, i.e., a U-phase arm 70u, a V-phase arm 70v, and a
W-phase arm 70w. The U-phase arm 70u comprises an upper arm device
72u having an upper switching device 74u (hereinafter referred to
as "upper SW device 74u") and a diode 76u, and a lower arm device
78u having a lower switching device 80u (hereinafter referred to as
"lower SW device 80u") and a diode 82u.
[0056] Similarly, the V-phase arm 70v includes an upper arm device
72v having an upper switching device 74v (hereinafter referred to
as "upper SW device 74v") and a diode 76v, and a lower arm device
78v having a lower switching device 80v (hereinafter referred to as
"lower SW device 80v") and a diode 82v. The W-phase arm 70w
includes an upper arm device 72w having an upper switching device
74w (hereinafter referred to as "upper SW device 74w") and a diode
76w, and a lower arm device 78w having a lower switching device 80w
(hereinafter referred to as "lower SW device 80w") and a diode
82w.
[0057] Each of the upper SW devices 74u, 74v, 74w and the lower SW
devices 80u, 80v, 80w comprises a MOSFET or an IGBT, for
example.
[0058] The phase arms 70u, 70v, 70w will hereinafter collectively
be referred to as "phase arms 70"). The upper arm devices 72u, 72v,
72w will hereinafter collectively be referred to as "upper arm
devices 72"), and the lower arm devices 78u, 78v, 78w will
hereinafter collectively be referred to as "lower arm devices 78").
The upper SW devices 74u, 74v, 74w will hereinafter collectively be
referred to as "upper SW devices 74", and the lower SW devices 80u,
80v, 80w will hereinafter collectively be referred to as "lower SW
devices 80"
[0059] In the phase arms 70, midpoints 84u, 84v, 84w between the
upper arm devices 72 and the lower arm devices 78 are connected
respectively to windings 86u, 86v, 86w of the electric motor 22.
The windings 86u, 86v, 86w will hereinafter collectively be
referred to as "windings 86".
[0060] The upper SW devices 74 and the lower SW devices 80 are
energized by respective drive signals UH, VH, WH, UL, VL, WL from
the ECU 50.
(c) Feedback System Sensors:
[0061] The current sensor 38 detects a current of the U-phase
(U-phase current Iu) in the winding 86u of the electric motor 22,
and outputs the detected U-phase current Iu to the ECU 50.
Similarly, the current sensor 40 detects a current of the W-phase
(W-phase current Iw) in the winding 86w of the electric motor 22,
and outputs the detected W-phase current Iw to the ECU 50. The
current sensors 38, 40 may detect currents in other phase
combinations than the U-phase and the W-phase as long as they
detect currents in two of the three phases of the electric motor
22.
[0062] The resolver 42 detects an electric angle .theta. as a
rotational angle of the output shaft 22a or an outer rotor (not
shown) of the electric motor 22, and outputs the detected electric
angle .theta. to the ECU 50.
[0063] The voltage sensor 44 detects a voltage at the midpoint 84u
of the U-phase arm 70u (hereinafter referred to as "U-phase voltage
Vu"), and outputs the detected U-phase voltage Vu to the ECU 50.
The voltage sensor 46 detects a voltage at the midpoint 84v of the
V-phase arm 70v (hereinafter referred to as "V-phase voltage Vv"),
and outputs the detected V-phase voltage Vv to the ECU 50. The
voltage sensor 48 detects a voltage at the midpoint 84w of the
W-phase arm 70w (hereinafter referred to as "W-phase voltage Vw"),
and outputs the detected W-phase voltage Vw to the ECU 50.
(d) ECU 50:
[0064] FIG. 3 shows in block form internal configurations and
functions of the ECU 50 and input and output lines connected to the
ECU 50. The ECU 50 controls output power of the electric motor 22
based on output values from the various sensors described
above.
[0065] As shown in FIGS. 1 and 3, the ECU 50 includes an
input/output unit 90, a processor 92, and a storage unit 94 as
hardware units. As shown in FIG. 3, the processor 92 of the ECU 50
includes an abnormality determining function (rotational speed
detecting unit) 100, an abnormal phase identifying function
(abnormal phase detecting unit) 102, and an energization
controlling function 104. The energization controlling function 104
includes a normal energization controlling function 106 and an
abnormality-occurring energization controlling function 108. These
functions are performed by executing programs stored in the storage
unit 94, as described in detail later.
(3) Battery 34:
[0066] The battery 34 is an electric energy storage device capable
of outputting a low voltage (12 volts in the present embodiment),
and may be a secondary battery such as a lead storage battery or
the like.
B. Processing Sequences and Functions of ECU 50
1. Overall Flow:
[0067] FIG. 4 is a flowchart of an overall processing sequence of
the ECU 50 according to the present embodiment. In step S1, the ECU
50 carries out a normal energization controlling mode using the
normal energization controlling function 106. In the normal
energization controlling mode, the ECU 50 controls output power of
the electric motor 22 using the three phase arms 70 (see FIG. 2) of
the inverter 36, as described in detail later.
[0068] In step S2, the ECU 50 (abnormality determining function
100) calculates a rotational speed .omega. [degrees/sec.] of the
electric motor 22 based on the electric angle .theta. from the
resolver 42.
[0069] In step S3, the ECU 50 (abnormality determining function
100) determines whether or not the rotational speed .omega.
calculated in step S2 is equal to or smaller than a threshold value
TH_.omega.. The threshold value TH_.omega. is a threshold value for
determining whether an abnormality determining process in step S4
is to be carried out or not. More specifically, the threshold value
TH_.omega. is a threshold value for determining whether or not the
electric motor 22 is generating an excessive counter-electromotive
force which makes the accuracy of the abnormality determining
process inadequate, and is stored in the storage unit 94.
[0070] If the rotational speed .omega. is not equal to or smaller
than the threshold value TH_.omega. (S3: NO), then control goes
back to step S1. If the rotational speed .omega. is equal to or
smaller than the threshold value TH_.omega. (S3: YES), then the ECU
50 carries out an abnormality determining process using the
abnormality determining function 100 in step S4. If the
determination result in step S4 indicates that no abnormality is
occurring (S5: NO), then control goes back to step S1.
[0071] If the determination result in step S4 indicates that an
abnormality is occurring (S5: YES), then the ECU 50 carries out an
abnormal phase identifying process in step S6. Based on the result
from the abnormal phase identifying process, the ECU 50 carries out
an abnormality-occurring energization controlling mode in step S7,
as described in detail later.
2. Normal Energization Controlling Mode (Normal Energization
Controlling Function 106):
[0072] FIG. 5 is a functional block diagram of the ECU 50 in the
normal energization controlling mode.
[0073] As shown in FIG. 5, the ECU 50 in the normal energization
controlling mode includes a torque command value calculator 110, a
phase compensator 112, a three-phase-to-dq converter (current
coordinate converting unit) 114, a q-axis current target value
calculator 116, a first subtractor 118, a q-axis PI controller
(voltage coordinate converting unit) 120, a d-axis current target
value setting section 122, a second subtractor 124, a d-axis PI
controller (voltage coordinate converting unit) 126, a
dq-to-three-phase converter 128, and a PWM controller 130. The ECU
50 controls the inverter 36 using these functional components.
[0074] The inverter 36 may basically be controlled by the control
system disclosed by JP 2009-090817 A1 or JP 2006-256542 A1, and
also components disclosed by JP 2009-090817 A1 or JP 2006-256542 A1
are additionally applicable to functional components which are
omitted in the present embodiment.
[0075] The torque command value calculator 110 calculates a torque
command value (hereinafter referred to as "first torque command
value Tr_c1") based on the steering torque Tr from the torque
sensor 28 and the vehicle speed V from the vehicle speed sensor 30.
The phase compensator 112 calculates a torque command value
(hereinafter referred to as "second torque command value Tr_c2") by
performing a phase compensation process on the first torque command
value Tr_c1.
[0076] The three-phase-to-dq converter 114 performs a
three-phase-to-dq converting process using the U-phase current Iu
from the current sensor 38, the W-phase current Iw from the current
sensor 40, and the electric angle .theta. from the resolver 42, and
calculates a d-axis current Id as a current component in a d-axis
direction (field current component) and a q-axis current Iq as a
current component in a q-axis direction (torque current component).
The three-phase-to-dq converter 114 outputs the q-axis current Iq
to the first subtractor 118 and outputs the d-axis current Id to
the second subtractor 124.
[0077] The three-phase-to-dq converting process is a process for
converting a set of the U-phase current Iu, the W-phase current Iw
and a V-phase current Iv, which is determined by the currents Iu,
Iw (i.e., Iv=-Iu-Iw), into a set of the d-axis current Id and the
q-axis current Iq according to a conversion matrix depending on the
electric angle .theta..
[0078] The q-axis current target value calculator 116 calculates a
target value for the q-axis current Iq (hereinafter referred to as
"q-axis current target value Iq_t") based on the second torque
command value Tr_c2 from the phase compensator 112, the vehicle
speed V from the vehicle speed sensor 30, the steering angle
.theta.s from the steering angle sensor 32, and the electric angle
.theta. from the resolver 42. More specifically, the q-axis current
target value calculator 116 calculates a q-axis current target
value Iq_t according to a combination of a reference assistive
control process, an inertia control process, and a damper control
process, for example. The reference assistive control process, the
inertia control process, and the damper control process may be the
control processes disclosed in JP 2009-090817 A1 and JP 2006-256542
A1 or Japanese Laid-Open Patent Publication No. 2009-214711, for
example. The q-axis current target value Iq_t serves as a
feed-forward command value for the d-axis current and the q-axis
current for causing the output shaft 22a of the electric motor 22
to generate a torque according to the second torque command value
Tr_c2.
[0079] The first subtractor 118 calculates the deviation between
the q-axis current target value Iq_t and the q-axis current Iq
(=Iq_t--Iq) (hereinafter referred to as "q-axis current deviation
.DELTA.Iq"), and outputs the calculated q-axis current deviation
.DELTA.Iq to the q-axis PI controller 120. The q-axis PI controller
120 calculates a target value for a q-axis voltage (hereinafter
referred to as "q-axis voltage target value Vq_t") according to a
PI control process (proportional-integral control process) as a
feedback control process such that the q-axis current deviation
.DELTA.Iq is reduced close to zero, and outputs the calculated
q-axis voltage target value Vq_t to the dq-to-three-phase converter
128.
[0080] The d-axis current target value setting section 122 sets a
target value for the d-axis current Id (hereinafter referred to as
"d-axis current target value Id_t") which is necessary for the
windings 86 of the electric motor 22 to function as a magnet, and
outputs the set d-axis current target value Id_t to the second
subtractor 124.
[0081] The second subtractor 124 calculates the deviation between
the d-axis current target value Id_t and the d-axis current Id
(=Id_t-Id) (hereinafter referred to as "d-axis current deviation
.DELTA.Id"), and outputs the calculated d-axis current deviation
.DELTA.Id to the d-axis PI controller 126. The d-axis PI controller
126 calculates a d-axis voltage target value Vd_t as a target value
for a d-axis voltage according to a PI control process
(proportional-integral control process) as a feedback control
process such that the d-axis current deviation .DELTA.Id is reduced
close to zero, and outputs the calculated d-axis voltage target
value Vd_t to the dq-to-three-phase converter 128.
[0082] The dq-to-three-phase converter 128 performs a
dq-to-three-phase converting process using the q-axis voltage
target value Vq_t from the q-axis PI controller 120, the d-axis
voltage target value Vd_t from the d-axis PI controller 126, and
the electric angle .theta. from the resolver 42, and calculates
voltage target values for the U-phase, the V-phase and the W-phase
(hereinafter referred to as "phase voltage target values Vu_t,
Vv_t, Vw_t"), and then the converter 128 outputs the calculated
phase voltage target values Vu_t, Vv_t, Vw_t to the PWM controller
130. The dq-to-three-phase converting process is a process for
converting a set of the d-axis voltage target value Vd_t and the
q-axis voltage target value Vq_t into a set of the phase voltage
target values Vu_t, Vv_t, Vw_t according to a conversion matrix
depending on the electric angle .theta..
[0083] Based on the phase voltage target values Vu_t, Vv_t, Vw_t,
the PWM controller 130 energizes the windings 86 of the electric
motor 22 through the inverter 36 according to a pulse width
modulation (PWM) control process. More specifically, the PWM
controller 130 selectively turns on and off the upper SW devices 74
and the lower SW devices 80 of the inverter 36 thereby to energize
the windings 86 of the electric motor 22.
[0084] Specifically, the PWM controller 130 generates drive signals
UH, UL, VH, VL, WH, WL for the phase arms 70 in each switching
period. If it is assumed that a duty ratio DUT in overall one
switching period is 100%, then a duty ratio DUT2 for the lower SW
devices 80 is calculated by subtracting a duty ratio DUT1 for the
upper SW devices 74 from 100%. Further, a dead time dt is reflected
in the duty ratios DUT1, DUT2 for the upper SW devices 74 and the
lower SW devices 80. Therefore, the drive signals UH, UL, VH, VL,
WH, WL that are actually output are representative of the duty
ratios DUT1, DUT2 with the dead time dt reflected therein.
[0085] According to the above normal energization controlling mode,
torques generated by the phases (hereinafter referred to as
"U-phase torque Tr_u", "V-phase torque Tr_v", "W-phase torque
Tr_w") in the normal energization controlling mode, a total torque
(hereinafter referred to as "motor torque Tr_m") output from the
electric motor 22 as the sum of the U-phase torque Tr_u, the
V-phase torque Tr_v and the W-phase torque Tr_w, and currents in
the phases (U-phase current Iu, V-phase current Iv, W-phase current
Iw) have waveforms as shown in FIG. 6, for example.
3. Abnormality Determining Process (Abnormality Determining
Function 100):
[0086] FIG. 7 is a flowchart of the abnormality determining process
(abnormality determining function 100) carried out by the ECU 50
(details of step S4 shown in FIG. 4). In step S11, the ECU 50
determines the d-axis voltage Vd and the q-axis voltage Vq by way
of calculations. More specifically, the ECU 50 performs a
three-phase-to-dq converting process on the U-phase voltage Vu from
the voltage sensor 44, the V-phase voltage Vv from the voltage
sensor 46, and the W-phase voltage Vw from the voltage sensor 48,
using the electric angle .theta., to determine the d-axis voltage
Vd and the q-axis voltage Vq.
[0087] In step S12, the ECU 50 determines whether the q-axis
voltage Vq determined in step S11 is greater than a threshold value
TH_Vq or not. The threshold value TH_Vq is a threshold value for
determining the q-axis voltage Vq is output or not.
[0088] If the q-axis voltage Vq is not greater than the threshold
value TH_Vq (S12: NO), the ECU 50 decides that no abnormality is
occurring in step S13, and control goes back to the processing
sequence shown in FIG. 4. If the q-axis voltage Vq is greater than
the threshold value TH_Vq (S12: YES), then control goes to step
S14.
[0089] In step S14, the ECU 50 determines whether the q-axis
current Iq is zero or not. The ECU 50 can thus determine whether
the q-axis current Iq is being generated or not. Instead of this
decision process, a positive threshold value may be established for
the absolute value of the q-axis current Iq, and the ECU 50 may
determine whether or not the q-axis current Iq is equal to or
smaller than the positive threshold value, thereby determining
whether a q-axis current Iq corresponding to the q-axis voltage Vq
is being generated or not.
[0090] If the q-axis current Iq is not zero (S14: NO), then control
goes to step S13. If the q-axis current Iq is zero (S14: YES), then
it is judged that no q-axis current Iq is flowing though the q-axis
voltage Vq is output. In this case, an abnormality is occurring
with no current flowing in either one of the phases (phase arms
70), e.g., one of the signal lines from the PWM controller 130 to
the SW devices 74, 80 is being disconnected. Then, the ECU 50
identifies the occurrence of an abnormality in step S15 (at this
time, which phase is suffering from the abnormality is not
identified).
4. Abnormal Phase Identifying Process (Abnormal Phase Identifying
Function 102):
[0091] FIG. 8 is a flowchart of an abnormal phase identifying
process (abnormal phase identifying function 102) carried out by
the ECU 50 (details of step S6 shown in FIG. 4). In step S21, the
ECU 50 determines whether the absolute value of a correlative
voltage between the V-phase voltage Vv from the voltage sensor 46
and the W-phase voltage Vw from the voltage sensor 48 (hereinafter
referred to as "VW interphase voltage Vvw") is lower than a
threshold value THv or not. The VW interphase voltage Vvw is
defined as the difference between the V-phase voltage Vv and the
W-phase voltage Vw (Vvw=Vv-Vw). The threshold value THv serves to
determine whether the VW interphase voltage Vvw is zero or is of a
value close to zero, i.e., whether the V-phase voltage Vv and the
W-phase voltage Vw are substantially equal to each other or
not.
[0092] If the absolute value of the VW interphase voltage Vvw is
smaller than the threshold value THv (S21: YES), then since VW
interphase voltage Vvw is substantially zero, the V-phase and the
W-phase are functioning properly. Therefore, it is decided that the
phase in which the abnormality is occurring is the U-phase. In step
S22, the ECU 50 identifies the U-phase as the phase in which the
abnormality is occurring. If the absolute value of the VW
interphase voltage Vvw is not smaller than the threshold value THv
(S21: NO), then control goes to step S23.
[0093] In step S23, the ECU 50 determines whether the absolute
value of a correlative voltage between the W-phase voltage Vw from
the voltage sensor 48 and the U-phase voltage Vu from the voltage
sensor 44 (hereinafter referred to as "WU interphase voltage Vwu")
is lower than the threshold value THv or not. The WU interphase
voltage Vwu is defined as the difference between the W-phase
voltage Vw and the U-phase voltage Vu (Vwu=Vw-Vu). The ECU 50 can
thus determine whether the WU interphase voltage Vwu is zero or is
of a value close to zero, i.e., whether the W-phase voltage Vw and
the U-phase voltage Vu are substantially equal to each other or
not.
[0094] If the absolute value of the WU interphase voltage Vwu is
smaller than the threshold value THv (S23: YES), then since WU
interphase voltage Vwu is substantially zero, the W-phase and the
U-phase are functioning properly. Therefore, it is decided that the
phase in which the abnormality is occurring is the V-phase. In step
S24, the ECU 50 identifies the V-phase as the phase in which the
abnormality is occurring. If the absolute value of the WU
interphase voltage Vwu is not smaller than the threshold value THv
(S23: NO), then control goes to step S25.
[0095] In step S25, the ECU 50 determines whether the absolute
value of a correlative voltage between the U-phase voltage Vu from
the voltage sensor 44 and the V-phase voltage Vv from the voltage
sensor 46 (hereinafter referred to as "UV interphase voltage Vuv")
is lower than the threshold value THv or not. The UV interphase
voltage Vuv is defined as the difference between the U-phase
voltage Vu and the V-phase voltage Vv (Vuv=Vu-Vv). The ECU 50 can
thus determine whether the UV interphase voltage Vuv is zero or is
of a value close to zero, i.e., whether the U-phase voltage Vu and
the V-phase voltage Vv are substantially equal to each other or
not.
[0096] If the absolute value of the UV interphase voltage Vuv is
smaller than the threshold value THv (S25: YES), then since UV
interphase voltage Vuv is substantially zero, the U-phase and the
V-phase are functioning properly. Therefore, it is decided that the
phase in which the abnormality is occurring is the W-phase. In step
S26, the ECU 50 identifies the W-phase as the phase in which the
abnormality is occurring. If the absolute value of the UV
interphase voltage Vuv is not smaller than the threshold value THv
(S25: NO), then the ECU 50 is unable to identify a phase in which
the abnormality is occurring (abnormal phase). In this case, two
phases may be suffering abnormalities which prevent currents from
flowing in the two phases. In step S27, the ECU 50 decides that it
is unable to identify an abnormal phase. The ECU 50 then shuts down
the electric motor 22 according to a fail-safe function
thereof.
5. Abnormality-Occurring Energization Controlling Mode
(Abnormality-Occurring Energization Controlling Function 108):
(1) Overall Arrangement:
[0097] FIG. 9 is a functional block diagram of the ECU 50 in the
abnormality-occurring energization controlling mode. Those
components shown in FIG. 9 which are identical to the components in
FIG. 5 are denoted by identical reference characters, and will not
be described in detail below.
[0098] As shown in FIG. 9, the ECU 50 in the abnormality-occurring
energization controlling mode includes a torque command value
calculator 110, a phase compensator 112, a gain setting section
140, an abnormal phase identifying function 102, a base voltage
calculator 142, a rotational speed calculator 144, a corrective
voltage calculator 146, a first adder 148, a second adder 150, a
third adder 152, and a PWM controller 130. The ECU 50 controls the
inverter 36 using these functional components.
(2) Torque Command Value Calculator 110 and Phase Compensator
112.
[0099] As with the normal energization controlling mode, the torque
command value calculator 110 calculates a first torque command
value Tr_c1 based on the steering torque Tr from the torque sensor
28 and the vehicle speed V from the vehicle speed sensor 30. The
phase compensator 112 calculates a second torque command value
Tr_c2 by performing a phase compensation process on the first
torque command value Tr_c1.
(3) Gain Setting Section 140:
[0100] FIG. 10 is a functional block diagram of the gain setting
section 140. The gain setting section 140 calculates a gain Gph
based on the second torque command value Tr_c2 and the vehicle
speed V. As shown in FIG. 10, the gain setting section 140 includes
an absolute value converter 160, an output voltage table 162 for
energizing two phases, a vehicle speed gain table 164 for
energizing two phases, a first multiplier 166, a rate limiting
processor 168, a sign converter 170, and a second multiplier
172.
[0101] The absolute value converter 160 calculates an absolute
value of the second torque command value Tr_c2 and outputs the
calculated absolute value to the output voltage table 162. The
output voltage table 162 for energizing two phases outputs an
output voltage Vout depending on the absolute value of the second
torque command value Tr_c2 to the first multiplier 166. The output
voltage Vout serves to set output power of the electric motor 22
depending on the second torque command value Tr_c2.
[0102] The vehicle speed gain table 164 for energizing two phases
outputs a ratio R1 depending on the vehicle speed V to the first
multiplier 166. The ratio R1 is used to reduce the output power of
the electric motor 22 to prevent the steering handle 12 from being
turned excessively when the vehicle speed V is high, for example.
The first multiplier 166 calculates a product Vout.times.R1 of the
output voltage Vout and the ratio R1, and outputs the product
Vout.times.R1 to the rate limiting processor 168. The product
Vout.times.R1 is of a value representing the steering torque Tr
applied by the driver with the vehicle speed V reflected
therein.
[0103] The rate limiting processor 168 adjusts a deviation .DELTA.D
between previous and present values of the product Vout.times.R1
such that the absolute value of the deviation .DELTA.D does not
exceed a positive threshold value TH_.DELTA.D. Specifically, if the
absolute value of the deviation .DELTA.D is equal to or smaller
than the threshold value TH_.DELTA.D, then the rate limiting
processor 168 outputs the deviation .DELTA.D as an updated value
P1. If the deviation .DELTA.D is of a positive value greater than
the threshold value TH_.DELTA.D, then the rate limiting processor
168 outputs the threshold value TH_.DELTA.D as an updated value P1.
If the deviation .DELTA.D is smaller than a value which is produced
by multiplying the threshold value TH_.DELTA.D by -1
(.DELTA.D<-TH_.DELTA.D), then the rate limiting processor 168
outputs the value which is produced by multiplying the threshold
value TH_.DELTA.D by -1 as an updated value P1.
[0104] The sign converter 170 outputs 1 when the second torque
command value Tr_c2 is positive, and outputs -1 when the second
torque command value Tr_c2 is negative. The sign converter 170
makes it possible to tell whether the steering handle 12 is turned
in one direction or the other (i.e., rotated to the left or
right).
[0105] The second multiplier 172 outputs the product of the updated
value P1 and the output value (-1 or 1) from the sign converter 170
as the gain Gph.
(4) Base Voltage Calculator 142:
[0106] As shown in FIG. 9, the base voltage calculator 142
calculates base voltages (hereinafter referred to as "base voltages
Vu_base, Vv_base, Vw_base") for the respective phases based on the
gain Gph, the electric angle .theta., and the identification result
(i.e., which phase is suffering from an abnormality) by the
abnormal phase identifying function 102.
[0107] Specifically, if the U-phase is suffering an abnormality,
then the base voltage calculator 142 calculates base voltages
Vu_base, Vv_base, Vw_base according to the expressions (1) through
(6) shown below. The base voltages Vu_base, Vv_base, Vw_base
represent phase voltage gains set depending on the steering action
made by the driver.
(a) For 0.degree..ltoreq..PHI.<180.degree.:
[0108] Vu_base=0 (1)
Vv_base=Gph.times.(1-0.5 sin .PHI.) (2)
Vw_base=-Gph.times.(1-0.5 sin .PHI.) (3)
(b) For 180.degree..ltoreq..PHI.<360.degree.:
[0109] Vu_base=0 (4)
Vv_base=Gph.times.(-1-0.5 sin .PHI.) (5)
Vw_base=-Gph.times.(-1-0.5 sin .PHI.) (6)
[0110] In the above expressions (1) through (6), .PHI. is defined
as the sum of the electric angle .theta. and 270.degree.
(.PHI.=.theta.+270.degree.) within the range of
0.degree..ltoreq..PHI.<360.degree.. The base voltages Vu_base,
Vv_base, Vw_base are indicated as shown in FIG. 11, for example. In
a case where the U-phase is suffering an abnormality, if control is
in the normal energization controlling mode (three-phase
energization controlling mode), then the electric motor 22 does not
generate a steering assisting force when the electric angle .theta.
is 90.degree. and 270.degree.. In the abnormality-occurring
energization controlling mode, however, as shown in FIG. 11, the
base voltages Vv_base, Vw_base are increased when the electric
angle .theta. is close to 90.degree. and 270.degree., making it
possible to reduce the effect of no steering assisting force
generated by the electric motor 22 when the electric angle .theta.
is 90.degree. and 270.degree..
[0111] If the V-phase is suffering an abnormality, then the base
voltage calculator 142 calculates base voltages Vu_base, Vv_base,
Vw_base according to the expressions (7) through (12) shown
below.
(c) For 0.degree..ltoreq..PHI.<180.degree.:
[0112] Vv_base=0 (7)
Vw_base=Gph.times.(1-0.5 sin .PHI.) (8)
Vu_base=-Gph.times.(1-0.5 sin .PHI.) (9)
(d) For 180.degree..ltoreq..PHI.<360.degree.:
[0113] Vv_base=0 (10)
Vw_base=Gph.times.(-1-0.5 sin .PHI.) (11)
Vu_base=-Gph.times.(-1-0.5 sin .PHI.) (12)
[0114] In the above expressions (7) through (12), .PHI. is defined
as the sum of the electric angle .theta. and 150.degree.
(.PHI.=.theta.+150.degree.) within the range of
0.degree..ltoreq..PHI.<360.degree.. The base voltages Vu_base,
Vv_base, Vw_base are indicated as shown in FIG. 12, for example. In
a case where the V-phase is suffering an abnormality, if control is
in the normal energization controlling mode (three-phase
energization controlling mode), then the electric motor 22 does not
generate a steering assisting force when the electric angle .theta.
is 30.degree. and 210.degree.. In the abnormality-occurring
energization controlling mode, however, as shown in FIG. 12, the
base voltages Vw_base, Vu_base are increased when the electric
angle .theta. is close to 30.degree. and 210.degree., making it
possible to reduce the effect of no steering assisting force
generated by the electric motor 22 when the electric angle .theta.
is 30.degree. and 210.degree..
[0115] If the W-phase is suffering an abnormality, then the base
voltage calculator 142 calculates base voltages Vu_base, Vv_base,
Vw_base according to the expressions (13) through (18) shown
below.
(e) For 0.degree..ltoreq..PHI.<180.degree.:
[0116] Vw_base=0 (13)
Vu_base=Gph.times.(1-0.5 sin .PHI.) (14)
Vv_base=-Gph.times.(1-0.5 sin .PHI.) (15)
(f) For 180.degree..ltoreq..PHI.<360.degree.:
[0117] Vw_base=0 (16)
Vu_base=Gph.times.(-1-0.5 sin .PHI.) (17)
Vv_base=-Gph.times.(-1-0.5 sin .PHI.) (18)
[0118] In the above expressions (13) through (18), .PHI. is defined
as the sum of the electric angle .theta. and 30.degree.
(.PHI.=.theta.+30.degree.) within the range of
0.degree..ltoreq..PHI.<360.degree.. The base voltages Vu_base,
Vv_base, Vw_base are indicated as shown in FIG. 13, for example. In
a case where the W-phase is suffering an abnormality, if control is
in the normal energization controlling mode (three-phase
energization controlling mode), then the electric motor 22 does not
generate a steering assisting force when the electric angle .theta.
is 150.degree. and 330.degree.. In the abnormality-occurring
energization controlling mode, however, as shown in FIG. 13, the
base voltages Vu_base, Vv_base are increased when the electric
angle .theta. is close to 150.degree. and 330.degree., making it
possible to reduce the effect of no steering assisting force
generated by the electric motor 22 when the electric angle .theta.
is 150.degree. and 330.degree..
(5) Rotational Speed Calculator 144:
[0119] The rotational speed calculator 144 shown in FIG. 9
calculates a rotational speed .omega. of the electric motor 22
based on the electric angle .theta. from the resolver 42.
(6) Corrective Voltage Calculator 146:
[0120] The corrective voltage calculator 146 calculates corrective
voltages (hereinafter referred to as "corrective voltages Vu_emf,
Vv_emf, Vw_emf") for the respective phases based on the electric
angle .theta., the rotational speed w, and the identification
result (i.e., which phase is suffering from an abnormality) by the
abnormal phase identifying function 102. The corrective voltages
Vu_emf, Vv_emf, Vw_emf serve to cancel out induced voltages
generated by the electric motor 22.
[0121] Specifically, if the U-phase is suffering an abnormality,
then the corrective voltage calculator 146 calculates corrective
voltages Vu_emf, Vv_emf, Vw_emf according to the expressions (19)
through (21) shown below.
Vu.sub.--emf=0 (19)
Vv.sub.--emf=-( 3/2)Ke.times..omega..times.sin .PHI. (20)
Vw.sub.--emf=( 3/2)Ke.times..omega..times.sin .PHI. (21)
[0122] In the above expressions (19) through (21), .PHI. is defined
as the sum of the electric angle .theta. and 270.degree.
(.PHI.=.theta.+270.degree.) within the range of
0.degree..ltoreq..PHI.<360.degree.. Ke represents an induced
voltage constant for one phase. " 3/2" represents a coefficient for
converting the induced voltage from a three-phase component into a
two-phase component.
[0123] If the V-phase is suffering an abnormality, then the
corrective voltage calculator 146 calculates corrective voltages
Vu_emf, Vv_emf, Vw_emf according to the expressions (22) through
(24) shown below.
Vv.sub.--emf=0 (22)
Vw.sub.--emf=-( 3/2)Ke.times..omega..times.sin .PHI. (23)
Vu.sub.--emf=( 3/2)Ke.times..omega..times.sin .PHI. (24)
[0124] In the above expressions (22) through (24), .PHI. is defined
as the sum of the electric angle .theta. and 150.degree.
(.PHI.=.theta.+150.degree.) within the range of
0.degree..ltoreq..PHI.<360.degree..
[0125] If the W-phase is suffering an abnormality, then the
corrective voltage calculator 146 calculates corrective voltages
Vu_emf, Vv_emf, Vw_emf according to the expressions (25) through
(27) shown below.
Vw.sub.--emf=0 (25)
Vu.sub.--emf=-( 3/2)Ke.times..omega..times.sin .PHI. (26)
Vv.sub.--emf=( 3/2)Ke.times..omega..times.sin .PHI. (27)
[0126] In the above expressions (25) through (27), .PHI. is defined
as the sum of the electric angle .theta. and 30.degree.
(.PHI.=.theta.+30.degree.) within the range of
0.degree..ltoreq..PHI.<360.degree..
(7) First Adder 148, Second Adder 150, and Third Adder 152:
[0127] In FIG. 9, the first adder 148 outputs the sum of the base
voltage Vu_base of the U-phase and the corrective voltage Vu_emf as
a U-phase voltage target value Vu_t to the PWM controller 130. The
second adder 150 outputs the sum of the base voltage Vv_base of the
V-phase and the corrective voltage Vv_emf as a V-phase voltage
target value Vv_t to the PWM controller 130. The third adder 152
outputs the sum of the base voltage Vw_base of the W-phase and the
corrective voltage Vw_emf as a W-phase voltage target value Vw_t to
the PWM controller 130.
(8) PWM Controller 130:
[0128] As with the normal energization controlling mode, the PWM
controller 130 energizes the windings 86 of the electric motor 22
through the inverter 36 according to a pulse width modulation (PWM)
control process based on the phase voltage command values Vu_t,
Vv_t, Vw_t. Specifically, the PWM controller 130 selectively turns
on and off the upper SW devices 74 and the lower SW devices 80 of
the inverter 36 to energize the windings 86 of the electric motor
22.
C. Advantages of the First Embodiment
[0129] According to the first embodiment, as described above, in a
state where the q-axis current Iq is zero (S14: YES in FIG. 7)
though the q-axis voltage Vq is being applied (S12: YES), a phase
other than a combination of phases whose interphase voltage is
nearly of nearly 0 volt is detected as an abnormal phase (see FIG.
8). Therefore, an abnormal phase can be detected even though only
two current sensors 38, 40 are used to detect phase currents.
[0130] According to the first embodiment, if the rotational speed
.omega. of the motor 22 is equal to or smaller than the threshold
value TH_.omega. (S3: YES in FIG. 4), the abnormality determining
process is carried out in step S4. In the case where a
counter-electromotive force generated by the electric motor 22
adversely affects the accuracy with which to identify an abnormal
phase, an abnormal phase is identified only when a certain level of
accuracy is secured. As a result, it is possible to prevent an
abnormal phase from being detected in error.
[0131] According to the first embodiment, if the ECU 50 detects an
abnormal phase (S5: YES in FIG. 4) while in the normal energization
controlling mode, the phases other than the abnormal phase are
energized such that the output power of the motor 22 are increased
in the vicinity of an electric angle .theta. at which the output
power of the electric motor 22 drops due to the malfunctioning of
the abnormal phase (see FIGS. 11 through 13). Therefore, even in
the presence of an abnormal phase, the output power of the electric
motor 22 is prevented from being abruptly lowered, and hence the
electric motor 22 is capable of stably generating a steering
assisting force.
II. Second Embodiment
A. Description of Configurations Differences with the First
Embodiment
[0132] The first embodiment and the second embodiment are different
from each other as to some parts of the software used by the ECU
50, but are identical to each other as to the hardware. Those
components of the second embodiment which are identical to those of
the first embodiment are denoted by identical reference characters,
and will not be described in detail below.
B. Processing Sequences and Functions of ECU 50
[0133] 1. Summary (Differences with the First Embodiment):
[0134] The first embodiment and the second embodiment are identical
to each other as to the overall processing flow of the ECU 50. The
flowchart shown in FIG. 4 and the functional block diagram shown in
FIG. 5 are also applicable to the second embodiment, except that
the second embodiment is different from the first embodiment in
processing details of step S4 shown in FIG. 4. Specifically, the
second embodiment uses an abnormality determining process shown in
FIG. 14, instead of the abnormality determining process shown in
FIG. 7 according to the first embodiment.
2. Abnormality Determining Process (Abnormality Determining
Function 100):
[0135] FIG. 14 is a flowchart of the abnormality determining
process (abnormality determining function 100) carried out by the
ECU 50 according to the second embodiment (details of step S4 shown
in FIG. 4). Steps S31 through S34 shown in FIG. 14 are the same as
steps S11 through S14 shown in FIG. 7 according to the first
embodiment.
[0136] In step S35 shown in FIG. 14, the ECU 50 stores an electric
angle .theta. at the time the q-axis current Iq is zero
(hereinafter referred to as "abnormality-occurring electric angle
.theta.1"). In step S36, the ECU 50 identifies the occurrence of an
abnormality (at this time, which phase is suffering from the
abnormality is not identified) as with step S15 shown in FIG.
7.
3. Abnormal Phase Identifying Process (Abnormal Phase Identifying
Function 102):
(1) Measuring Principles:
[0137] The abnormal phase identifying process (step S6 in FIG. 4)
according to the second embodiment identifies an abnormal phase
based on the fact that in the event of an abnormality such as a
disconnection or the like in any of the phases, no current flows in
the electric motor 22 at an electric angle .theta. inherent in the
phase.
[0138] Specifically, if the U-phase is suffering an abnormality
while no d-axis voltage Vd is being output (Vd=0), then the
electric angle .theta. at which no current flows in the electric
motor 22 is 90.degree. and 270.degree.. If the V-phase is suffering
an abnormal while no d-axis voltage Vd is being output, then the
electric angle .theta. at which no current flows in the electric
motor 22 is 30.degree. and 210.degree.. If the W-phase is suffering
an abnormality while no d-axis voltage Vd is being output, then the
electric angle .theta. at which no current flows in the electric
motor 22 is 150.degree. and 330.degree.. The electric angle .theta.
at which no current flows in the electric motor 22 on account of an
abnormal phase while no d-axis voltage Vd is being output will
hereinafter be referred to as "base electric angle .theta.b1".
[0139] While the d-axis voltage Vd is being output (Vd.noteq.0),
since motor terminal voltages of the respective phases deviate from
each other, the electric angle .theta. at which no current flows in
the electric motor 22 deviates from the base electric angle
.theta.b1. If the d-axis voltage Vd is zero while the U-phase is
suffering an abnormality, the V-phase current Iv and the W-phase
current Iw are indicated as shown in FIG. 15, for example. If the
d-axis voltage Vd is not zero while the U-phase is suffering an
abnormality, the V-phase current Iv and the W-phase current Iw are
indicated as shown in FIG. 16, for example.
[0140] According to the second embodiment, if the q-axis current Iq
is zero though the d-axis voltage Vd is being output, the electric
angle .theta. (abnormality-occurring electric angle .theta.1) at
the time is stored, and a deviation from the base electric angle
.theta.b1 (hereinafter referred to as "corrective electric angle
.theta.c") is identified. It is then determined whether a phase to
be judged is suffering an abnormality or not based on whether an
electric angle .theta. (corrected electric angle .theta.b2)
produced by correcting the base electric angle .theta.b1 with the
corrective electric angle Bc is in agreement with the
abnormality-occurring electric angle .theta.1 or not.
(2) Process of Identifying Corrective Electric Angle .theta.c:
[0141] If the d-axis voltage Vd is not zero, then a corrective
electric angle .theta.c can be indicated as the phase of a combined
vector of the d-axis voltage Vd and the q-axis voltage Vq (see FIG.
17). Therefore, a corrective electric angle .theta.c can be
identified if the relationship between d-axis voltages Vd and
q-axis voltages Vq, and corrective electric angles .theta.c is
determined in advance and stored as a map.
(3) Flow of Abnormal Phase Identifying Process:
[0142] FIG. 18 is a flowchart of an abnormal phase identifying
process (abnormal phase identifying function 102) carried out by
the ECU 50 according to the second embodiment. In step S41 shown in
FIG. 18, the ECU 50 identifies a corrective electric angle .theta.c
based on the d-axis voltage Vd and the q-axis voltage Vq (see FIG.
17).
[0143] In step S42, the ECU 50 calculates corrected base electric
angles .theta.b2 for the respective phases. More specifically,
since the base electric angles .theta.b1 of the U-phase are
90.degree. and 270.degree., the corrected base electric angles
.theta.b2 are 90.degree.-.theta.c and 270.degree.-.theta.c. Since
the base electric angles .theta.b1 of the V-phase are 30.degree.
and 210.degree., the corrected base electric angles .theta.b2 are
30.degree.-.theta.c and 210.degree.-.theta.c. Since the base
electric angles .theta.b1 of the W-phase are 150.degree. and
330.degree., the corrected base electric angles .theta.b2 are
150.degree.-.theta.c and 330.degree.-.theta.c. For illustrative
purposes, the two corrected base electric angles .theta.b2 for the
U-phase will be referred to as "corrected base electric angles
.theta.u1, .theta.u2", the two corrected base electric angles
.theta.b2 for the V-phase as "corrected base electric angles
.theta.v1, .theta.v2", and the two corrected base electric angles
.theta.b2 for the W-phase as "corrected base electric angles
.theta.w1, .theta.w2".
[0144] In step S43, the ECU 50 determines whether or not the
abnormality-occurring electric angle .theta.1 is either one of the
corrected base electric angles .theta.u1, .theta.u2 of the U-phase.
If the abnormality-occurring electric angle .theta.1 is either one
of the corrected base electric angles .theta.u1, .theta.u2 of the
U-phase (S43: YES), then it is judged that the U-phase is suffering
an abnormality such as a disconnection or the like. In step S44,
the ECU 50 identifies the U-phase as suffering an abnormality. If
the abnormality-occurring electric angle .theta.1 is neither the
corrected base electric angle .theta.u1 nor .theta.u2 of the
U-phase (S43: NO), then control goes to step S45.
[0145] In step S45, ECU 50 determines whether or not the
abnormality-occurring electric angle .theta.1 is either one of the
corrected base electric angles .theta.v1, .theta.v2 of the V-phase.
If the abnormality-occurring electric angle .theta.1 is either one
of the corrected base electric angles .theta.v1, .theta.v2 of the
V-phase (S45: YES), then it is judged that the V-phase is suffering
an abnormality such as a disconnection or the like. In step S46,
the ECU 50 identifies the V-phase as suffering an abnormality. If
the abnormality-occurring electric angle .theta.1 is neither the
corrected base electric angle .theta.v1 nor .theta.v2 of the
V-phase (S45: NO), then control goes to step S47.
[0146] In step S47, ECU 50 determines whether or not the
abnormality-occurring electric angle .theta.1 is either one of the
corrected base electric angles .theta.w1, .theta.w2 of the W-phase.
If the abnormality-occurring electric angle .theta.1 is either one
of the corrected base electric angles .theta.w1, .theta.w2 of the
W-phase (S47: YES), then it is judged that the W-phase is suffering
an abnormality such as a disconnection or the like. In step S48,
the ECU 50 identifies the W-phase as suffering an abnormality. If
the abnormality-occurring electric angle .theta.1 is neither the
corrected base electric angle .theta.w1 nor .theta.w2 of the
W-phase (S47: NO), then the ECU 50 is unable to identify a phase in
which the abnormality is occurring (abnormal phase). In this case,
two phases may be suffering abnormalities which prevent currents
from flowing in the two phases. In step S49, the ECU 50 decides
that it is unable to identify an abnormal phase. The ECU 50 then
shuts down the electric motor 22 according to a fail-safe function
thereof.
[0147] In the processing sequence shown in FIG. 18, the ECU 50
determines whether the abnormality-occurring electric angle
.theta.1 is in agreement with the corrected base electric angle
.theta.b2 of each phase or not. It is possible to perform a
sequence in view of a measuring error. For example, a range defined
by two threshold values on both sides of the corrected base
electric angle .theta.u1 of the U-phase, for example, may be
established, and if the abnormality-occurring electric angle
.theta.1 falls within the range thus defined, then the ECU 50 can
identify the U-phase as suffering an abnormality such as a
disconnection or the like.
4. Abnormality-Occurring Energization Controlling Mode
(Abnormality-Occurring Energization Controlling Function 108):
[0148] In the second embodiment, the ECU 50 in the
abnormality-occurring energization controlling mode has the same
functions as with the first embodiment (see FIGS. 9 through 13 and
the description relevant thereto).
C. Advantages of the Second Embodiment
[0149] According to the second embodiment, as described above, the
ECU 50 calculates a corrected base electric angle .theta.b2 (S42 in
FIG. 18) at which the q-axis current Iq is zero (S34: YES in FIG.
14) though the q-axis voltage Vq is being applied (S32: YES), and
determines an abnormal phase based on the corrected base electric
angle .theta.b2 (S43 through S49). Therefore, an abnormal phase can
be detected even though only two current sensors 38, 40 are used to
detect phase currents.
[0150] According to the second embodiment, a corrective electric
angle .theta.c is identified based on the d-axis voltage Vd and the
q-axis voltage Vq (see FIG. 17), and an abnormal phase is
determined based on the base electric angle .theta.b1 and the
corrective electric angle .theta.c. Therefore, even if the electric
angle .theta. at which the q-axis current Iq is zero due to the
generation of the d-axis voltage Vd deviates from the base electric
angle .theta.b1 (see FIG. 16), it is possible to correct the base
electric angle .theta.b1 in view of the effect of the d-axis
voltage Vd. Therefore, an abnormal phase can be determined highly
accurately.
[0151] According to the second embodiment, if the rotational speed
.omega. of the motor 22 is equal to or smaller than the threshold
value TH_.omega. (S3: YES in FIG. 4), the abnormality determining
process is carried out in step S4. In the case where a
counter-electromotive force generated by the electric motor 22
adversely affects the accuracy with which to identify an abnormal
phase, an abnormal phase is detected only when a certain level of
accuracy is secured. As a result, it is possible to prevent an
abnormal phase from being detected in error.
III. Modifications
[0152] The present invention is not limited to the above
embodiments, but may adopt various arrangements based on the
contents of the present description. For example, the present
invention may adopt the following arrangements:
A. Identification of Abnormal Phase:
[0153] In the above embodiments, it is determined whether an
abnormality is occurring in any of the phases or not based on
whether or not the q-axis current Iq is zero (S14 in FIG. 7 and S34
in FIG. 14). However, a positive threshold value and a negative
threshold value near zero may be established, and it may be
determined whether an abnormality is occurring in any of the phases
or not based on whether or not the q-axis current Iq falls between
the positive threshold value and the negative threshold value.
Alternatively, it may be determined whether an abnormality is
occurring in any of the phases or not based on whether or not the
absolute value of the q-axis current Iq is equal to or smaller than
a positive threshold value near zero.
[0154] In the second embodiment, an abnormal phase is determined
using the corrected electric angle .theta.b2 which is produced by
reflecting the corrective electric angle .theta.c in the base
electric angle .theta.c. However, an abnormal phase may be
determined using the base electric angle .theta.b1 only when no
d-axis voltage Vd is generated.
B. Modifications of Output Forms of Various Values in the
Abnormality-Occurring Energization Controlling Mode:
[0155] FIGS. 19 through 24 show first through sixth modifications
with respect to the relationship between electric angles .theta. of
the electric motor 22 and output voltages for the respective phases
in the abnormality-occurring energization controlling mode. Stated
otherwise, FIGS. 19 through 24 show modifications of the processing
sequence of the gain setting section 140 (see FIG. 9). In FIGS. 19
through 24, it is assumed that the W-phase is suffering a
disconnection.
[0156] FIG. 19 shows an example in which the U-phase voltage Vu and
the V-phase voltage Vv are output in trapezoidal waveforms
depending on the electric angle .theta., the second torque command
value Tr_c2 and the vehicle speed V.
[0157] FIG. 20 shows an example in which the U-phase voltage Vu and
the V-phase voltage Vv are output in waveforms represented by
"(1-0.5 sin .theta.)" depending on the electric angle .theta., the
second torque command value Tr_c2 and the vehicle speed V.
[0158] FIG. 21 shows an example in which the U-phase voltage Vu and
the V-phase voltage Vv are output in waveforms represented by
"1/cos(.theta.-60.degree.)" depending on the electric angle
.theta., the second torque command value Tr_c2 and the vehicle
speed V. However, a limiting control process, i.e., a control
process for providing an upper limit value and a lower limit value,
is carried out for voltages that are higher than 1.5 times the
maximum voltage in the normal energization controlling mode.
[0159] FIG. 22 shows an example in which the U-phase voltage Vu and
the V-phase voltage Vv are output in waveforms represented by
"1/cos(.theta.-60.degree.)" depending on the electric angle
.theta., the second torque command value Tr_c2 and the vehicle
speed V. However, a limiting control process is carried out for
voltages that are higher than twice the maximum voltage in the
normal energization controlling mode.
[0160] FIG. 23 shows an example in which the U-phase voltage Vu and
the V-phase voltage Vv are output in waveforms represented by
"1/cos(.theta.-60.degree.)" depending on the electric angle
.theta., the second torque command value Tr_c2 and the vehicle
speed V. However, a limiting control process is carried out for
voltages that are higher than three times the maximum voltage in
the normal energization controlling mode.
[0161] FIG. 24 shows an example in which the U-phase voltage Vu and
the V-phase voltage Vv are output in waveforms represented by
"1/cos(.theta.-60.degree.)" depending on the electric angle
.theta., the second torque command value Tr_c2 and the vehicle
speed V.
C. Application of Rotational Speed .omega. of Electric Motor
22:
[0162] In the above embodiments, the rotational speed .omega. and
the threshold value TH_.omega. are compared with each other, and
the abnormality determining process (S4) is carried out only when
the rotational speed .omega. is equal to or smaller than the
threshold value TH_.omega. (S3: YES in FIG. 4). However, it is
possible to use an arrangement which does not compare the
rotational speed .omega. and the threshold value TH_.omega. with
each other.
[0163] Although certain preferred embodiments of the present
invention have been shown and described in detail, it should be
understood that various changes and modifications may be made
therein without departing from the scope of the appended
claims.
* * * * *